Natural gas is an energy source that may decrease the reliance on liquid fuel for power generation. However, many natural gas reservoirs contain a complex mixture of acid gases (e.g., carbon dioxide, and hydrogen sulfide), higher value heavy hydrocarbons, inert gases, and trace components of many other compounds. In many natural gas reserves, carbon dioxide (CO2) and hydrogen sulfide (H2S) can be present in the high quantities. At high concentrations, CO2 or H2S in combination with water is corrosive, and, therefore, can destroy pipelines or other equipment. Furthermore, the presence of CO2 reduces the heating value of natural gas. Therefore, natural gas from natural gas reservoirs or “produced gas” is processed prior to distribution and usages. The bulk removal of these gases will decrease the post-membrane treatment units (such as acid gas amine scrubbing and cryogenic condensation) and will increase the feed gas quality and flow.
Membrane technology has become an essential alternative for efficient gas separation process. Due to the manufacturability, low material costs, robust physical characteristics, and good intrinsic transport properties, as compared to the conventional method for acid gas separation (for example, acid gas amine scrubbing), polymeric membranes are of great research interest in the membrane technology field. However, polymeric membranes designed for gas separations are known to have a trade-off between permeability and selectivity. In addition, there are other significant material challenges, such as physical aging and plasticization.
Glassy polymers, such as cellulose acetate (CA), polyimide PI), and polysulfone (PSF), are used for sour gas removal from natural gas, due to their high thermal stability. CA polymer membranes may be used for CO2 separation and exhibit high pure gas carbon dioxide/methane (CO2/CH4) selectivity of approximately 30. However, due to easy plasticization at high CO2 pressure or in the presence of significant amounts of higher-hydrocarbon contaminants, glassy polymers, such as CA, exhibit much lower CO2/CH4 mixed gas selectivities and exhibit very low CO2 permeability (approximately 5 Barrer=3.75×10−17 m2·s−1·Pa−1), which does not meet some industrial requirements. Similarly, another commercially available polyimide exhibits higher CO2/CH4 pure gas selectivity of 40, but still much lower CO2 permeability of less than 12 Barrer (=9.00×10−17 m2·s−1·Pa−1).